Recently, an electric vehicle and a hybrid vehicle having a system for moving a vehicle with a motor become popular in view of environmental consciousness. A general electric construction of these vehicles is shown in FIG. 9. A smoothing capacitor C1 and an inverter circuit 2 are connected between both ends of a battery 1. A motor 3 for moving a vehicle is controlled by the inverter circuit 2. Further, Another smoothing capacitor C2 and an electric device 4 are connected between both ends of the smoothing capacitor C1 via inductors L1, L2. The electric device 4 is, for example, a vehicular electronic apparatus or an auxiliary electronic apparatus such as a battery charger when the vehicle is the electric vehicle.
The inverter circuit 2 generates noise when the circuit 2 executes a switching operation of large current. When the noise penetrates into the electric device 4, an operation failure may be occurred. Thus, in order to restrict the noise from penetrating, the inductors L1, L2 are arranged on a power source line between the battery 1 and the electric device 4, or a filter is provided by an inductance component in the power source line.
When the inductors L1, L2 are arranged in the power source line, a parasitic LC resonance may occur between the battery 1 or the smoothing capacitor C1 and the other smoothing capacitor C2 on the electric device side. Therefore, heat may generate since the large resonant current flows through the smoothing capacitor C2. Accordingly, it is necessary to restrict the resonance between the capacitors C1, C2.
JP-2000-295771 A teaches a technique for restricting the resonance. In JP-2000-295771 A, a capacitor is connected to an inverter circuit, and another capacitor is connected to a portion (on an output side of a rectifying circuit) facing the inductor. The capacitor and the other capacitor are connected in series to a secondary winding of a transformer. A voltage in proportion to a load current is applied to a primary winding of the transformer, so that the resonance is restricted.
Here, assuming that the construction described in JP-2000-295771 A is combined with the system in FIG. 9, the transformer may be arranged at one of points A to E in FIG. 9 disposed on a resonant passage. However, since conduction loss of the transformer, generated in a case where the windings are energized, is large, an efficiency may be not high. Further, even if the transformer is arranged at one of five points, the following difficulties may occur.
For example, when the transformer is arranged at the point A, the resonance at the capacitor C1 is restricted. However, the resonance generated on a passage between the battery 1 and the capacitor C2 via the inductor L1 is not restricted.
Further, when the transformer is arranged at the point B, and the point B is disposed on a passage of an input current to the inverter circuit 2, the input current is detected, and the voltage is applied to the transformer, so that the power source voltage to be supplied to the inverter circuit 2 may be reduced. Further, the inverter circuit 2 turns on and off the input current while the circuit 2 executes the switching operation. In general, a large parasitic inductance may be provided by the transformer. Thus, a large switching surge may occur when the circuit 2 turns on and off the input current.
When the transformer is arranged at the point C or the point E, it is necessary to form a gap at a core of the transformer since the direct current flows through the transformer. Thus, since large invalidation current (i.e., wattles current) flows through a structure for applying the voltage to the transformer, the efficiency may be reduced, and the size of circuit elements to be used on the structure may increase.
When the transformer is arranged at the point D, the current of the capacitor C2 is drawn into the point D when the consumption current of the electric device 4 is changed transitionally. Accordingly, similar to the point B, the power source voltage to be supplied to the inerter circuit 2 may be reduced. When the electric device 4 turns on and off the input current, the large switching surge may be generated according to the switching operation of the electric device 4.